WHERE ARE WE?
TAFIRI
Mandela
DSFA
ZAFIRI
2025-07-14
For Yellowfin, Bigeye, and Skipjack tuna.
Length-Based Spawning Potential Ratio (LBSPR)
\[ \begin{align} SPR &= \frac{\text{Fished}}{\text{Unfished}} \\ &= \frac{\sum_{L} \phi(L) \cdot F(L)}{\sum_{L} \phi_0(L) \cdot F(L)} \end{align} \]
Neritic waters
Data from the neritic zone were sourced from both TAFIRI and DSFA
EEZ
Data from Exclusive Economic Zone were sourced from DSFA
“The sampling spans all 12 months of 2024, ensuring comprehensive coverage. Data was collected consistently from January through December.”
Yellowfin tuna
Skipjack tuna
Bigeye tuna
All three assessed tuna stocks are within the recommended range of sustainable levels.
The Spawning Potential Ratio (SPR) for all species is above 20% but below the 40% target reference point.
The primary driver is the harvest of immature fish: The size at which fish are caught (\(SL_{50}\)) is consistently and significantly lower than the size at which they mature (\(L_{50}\)).
The consistent gap between size at maturity (\(L_{50}\)) and size at capture (\(SL_{50}\)) is a major red flag.
| Species | Spawning Potential (SPR) | Size at Maturity (\(L_{50}\)) | Size at Capture (\(SL_{50}\)) | Status |
|---|---|---|---|---|
| Yellowfin | 29% | 92.3 cm | 59.5 cm | Sustainable |
| Bigeye | 33% | 82.0 cm | 62.7 cm | Sustainable |
| Skipjack | 33% | 59.9 cm | 50.2 cm | Sustainable |
An SPR range between 20% and 40% is the recommended.
The Core Problem: the average size at capture is significantly smaller than the size at maturity.